Space heating and cooling systems typically include a refrigerant circulated by a compressor through finned pipes located inside and outside a building. In winter, the compressor forces compressed and warmed refrigerant into finned pipe sections within the house where condensation takes place. The liberated heat is usually dispensed into the house by means of a fan. The condensed refrigerant then passes through a throttle valve to an evaporator. The heat of evaporation is provided by the colder outside air. During summer, the sense of circulation of the refrigerant is reversed. The outside finned pipes constitute the condenser, while the inside finned pipes operate as the evaporator.